The thermal decomposition kinetics of high iron gibbsite ore was investigated under non-isothermal conditions. Popescu method was applied to analyzing the thermal decomposition mechanism. The results show that the most probable thermal decomposition mechanism is the three-dimensional diffusion model of Jander equation, and the mechanism code is D3. The activation energy and pre-exponential factor for thermal decomposition of high iron gibbsite ore calculated by the Popescu method are 75.36 kJ/mol and 1.51×10⁵s^-1, respectively. The correctness of the obtained mechanism function is validated by the activation energy acquired by the iso-conversional method. Popescu method is a rational and reliable method for the analysis of the thermal decomposition mechanism of high iron gibbsite ore.